As a reading element of a thin film magnetic head, an MR element configured with a multilayer film has been known. Conventionally, a current in plane (CIP) element where a sense current flows in a direction within a film plane has been mostly utilized. Recently, in order to correspond further high density recording, a current perpendicular to the plane (CPP) element where a sense current flows in a direction orthogonal to a film surface has been developed. As this type of element, a tunnel magneto-resistance (TMR) element to which a TMR effect is used and a CPP-giant magneto resistance (GMR) element to which a GMR effect is used are known.
An example of the GMR element or the TMR element is an element provided with a spin valve film (hereinafter, referred to as a SV film). The SV film is a multilayer film including a pinning layer, a pinned layer, a spacer layer and a free layer. The pinned layer is a ferromagnetic layer of which a magnetization direction is pinned against an external magnetic field. The free layer is a ferromagnetic layer of which a magnetization direction changes according to an external magnetic field. The spacer layer is sandwiched between the pinned layer and the free layer. The pinning layer is disposed for pinning the magnetization direction of the pinned layer, and typically is configured with an anti-ferromagnetic layer. The SV film is sandwiched by a pair of shields that are electrodes for supplying a sense current.
In a typical MR element, as disclosed in U.S. Pat. No. 7,817,381B2, hard magnetic layers are disposed on both sides of a SV film in a track width direction with insulating films therebetween. The hard magnetic layer is referred to as a bias magnetic layer. This bias magnetic layer applies a bias magnetic field to the free layer to change the free layer to a single magnetic domain. Changing the free layer to a single magnetic domain increases a linearity of a resistance change according to the change of an external magnetic field and also is advantageous for suppressing the Barkhausen noise. The magnetization direction of the bias magnetic layer is pinned in the track width direction. In the present specification, the track width direction means a direction parallel to a direction that defines a track width of a recording medium when a slider including the MR element faces the recording medium.
However, in correspondence with the improvement of a recording density of recent magnetic recording media, a side reading problem, which a magnetic head reads magnetic information leaking from adjacent tracks, occurs.
In order to cope with the side reading problem, U.S. Patent Application Publication No. 2005/0270702A1 discloses a thin film magnetic head provided with soft magnetic layers on both sides of an MR element in the track width direction. Since a soft magnetic material absorbs a magnetic flux from adjacent tracks, a noise effect due to the magnetic flux from the adjacent tracks is suppressed. As a result, a thin film magnetic head that is compatible with a recording medium of high recording density can be provided.
However, the soft magnetic layer has no function that applies a bias magnetic field to the MR element. Accordingly, in U.S. Patent Application Publication 2005/0270702A1, the MR element includes two free layers of which magnetization directions change according to an external magnetic field and an antiferromagnetic coupling layer disposed between the free layers, and the antiferromagnetic coupling layer let one free layer and the other free layer antiferromagnetically interact to each other. With such a structure, the antiferromagnetic coupling layer provides a self bias function to both of the free layers. However, with such a bias function, sufficient bias is occasionally not applied to the free layers. Further, since only specific materials can be used for the antiferromagnetic coupling layer as a spacer, it becomes difficult to improve the performance of the MR element.
As described above, it is difficult to apply sufficient bias to the free layers while the function of side shield is maintained. As a result, a thin film magnetic head that can apply sufficient bias to the free layers while the function of the side shield is maintained and a method of manufacturing the thin film magnetic head are desired to provide.